Southern yellow pine (Pinus sp.) wood cubes were vacuum-pressure treated with nano-SiO2 solution and different concentrations of amine copper quaternary (ACQ)/wax (0.5%, 2.5%, and 5.0% wax)-modified solutions. The effects of wax concentration and nano-SiO2 addition on water absorption, air drying shrinkage, and moisture swelling stabilities were investigated. The results showed that during the whole process of water absorption and air drying shrinkage, better stability of nano-SiO2 modified ACQ-treated wood could only be obtained with the ratio of wax addition equal to 2.5%. However, the best moisture swelling resistance was found in the samples modified with the highest wax addition (5.0%). Both wax and nano-SiO2 could be useful for keeping the dimensional stability of the treated wood.